Color electrophotographic (EP) printers can be implemented in several different configurations. One large class of electrophotographic printers includes those that have the ability to develop the final image at nearly the same process speed as that of a single developer. These are “single-pass” or “tandem” printers, which use one photoconductor (PC) and one developer for each color as shown in FIG. 1. In this configuration, photoconductors 10-13 contact a separate region of a transfer drum or belt 14. Developers 15-18 respectively develop latent images on photoconductors 10-13. As in electrophotography, each developer tones the latent image on a respective photoconductor, and the toner may be subsequently transferred to an intermediate 14 such as a transfer belt or drum. The development is timed so that as the first image on the intermediate 14 arrives under the second photoconductor, the two color separations are aligned. This sequence-continues, color by color, until the image is complete. The toner is then transferred in one step to the desired media. Since the imaging process for each color is independent, the media can be sent through, one after another, with a minimal gap in between the sheets of media. Thus, the printer process speed is close to that of a single developer. Other embodiments of single-pass printers may provide developed images upon media without an intermediate.
Another class of electrophotographic printers includes those that develop the image on a single photoconductor in a sequence and may be referred to as “multi-pass” color printers. In these configurations, all of the colors are transferred to the substrate one by one before the next piece of media can be sent through. Accordingly, for a four-color printer, the process speed of the printer will be approximately one-fourth that of the developer. Although the multi-pass printer is considerably slower than the single-pass at the same developer speed, the multi-pass configuration has certain advantages. For example, a lower cost is possible since only a single charging and imaging system is utilized. Further, in at least one multi-pass system, all colors are provided to the photoconductor before application to the media substrate. Color plane alignment is generally improved compared with a single-pass system where the images on different drums are aligned with one another.
In a second variation of a multi-pass printer, the image is transferred to an intermediate, such as a belt. However, the plane-to-plane registration can be relatively poor for a belt embodiment. If the transfer is to an intermediate drum, the registration can approach results achievable with the above-mentioned accumulating photoconductor drum.
Some multi-pass embodiments enable the use of a relatively small photoconductor and which can have reduced cost if implemented as an organic imaging region using “beer can” dip-coat technology. To the contrary, photoconductor drums of relatively increased size are typically machined from aluminum to retain sufficient rigidity. The final product therefore is more costly regardless of whether the imaging region is organic or amorphous silicon (a-Si), for example.
Referring to FIG. 2, a multi-pass color printer configuration may include a rotating carousel 20 which houses several developers (not shown). The first developer is placed adjacent to the photoconductor 21 for development of a latent image. The developed image can then be transferred to an intermediate or retained in place for subsequent layers. After the first layer is developed, the second developer is rotated into place. Development continues until all the colors are deposited on the photoconductor or the intermediate.
Referring to FIG. 3, another configuration provides a multi-pass printer implemented with developers 30-33 aligned around a periphery of the photoconductor 34. Unlike the carousel arrangement described above, individual developers advance towards photoconductor 34 to develop an image (i.e., developer 33 shown in FIG. 3) and retract after development (i.e., developers 30-32 in FIG. 3). The configuration of FIG. 3 saves time between development of colors and enables utilization of a more straightforward developer design since the developer housings are not rotated.
While the peripheral-developer multi-pass configuration of FIG. 3 described above offers advantages over the carousel configuration of FIG. 2, the configuration of FIG. 3 has associated drawbacks of utilizing a relatively large photoconductor to accommodate the developers provided around the periphery. In addition, room around the periphery is provided for cleaner, charger and imager systems, as well as dead space enabling the photoconductor to respond to imaging light. Accordingly, compared to the single-pass color printer of FIG. 1, the photoconductor of the peripheral-developer multi-pass color printer of FIG. 3 is typically larger in diameter. In the embodiment of FIG. 3, it is common to provide a photoconductor of sufficient size to receive an entire image for color development. In some embodiments, the photoconductor length may be increased to twice the media size to simultaneously accommodate two images.
Although use of a large photoconductor of a peripheral-developer multi-pass printer may appear to be a costly disadvantage, there are instances where the configuration of FIG. 3 is worthwhile. For example, a six-color printer, useful for high quality photographs, utilizes two additional developers, and if a carousel is implemented, the extra developer modules may render the developer assembly rather unwieldy. The photoconductor drum of the embodiment of FIG. 3 may be sized to accommodate the additional developers. However, at some point, the photoconductor drum even in the configuration of FIG. 3 may become too large for cost effective fabrication.
At least some aspects of the disclosure provide improved methods and apparatus for generating images upon media.